High-temperature steel



Patented Mar. 10, 1953 UNITED STATES 2,631,096 HIGH-TEMPERATURE screen DarwynLBrown, llastings-nnefludson, 10.2., s, signor toU'nited States Steel Corporatioma corporation ofNew Jersey No Drawing. Application February 1, 195 1,

-- Serial'Now 208,983

1 Claim. W (c1. 75-123) This invention relates to steels for elevated I temperature service having improved hardenability characteristics.

The medium alloy ferritic or pearliticisteels. used for elevated temperature service usually contain sufi'icient molybdenum to give enhanced creep resistance. A commonly used grade of this steel contain from .05 to .20% carbon, .15 to .50% manganese, .05 to 30% silicon,f .40 to .60% molybdenum, 25% balance iron except for residual amounts of other elements and impurities. Such composition provides -mflst. of the mechanical properties needed for; pressure vessels but the highrhardenability thereof renders it 15 unsuitable for use in structures subjected to dynamic loading after the steel has been rapidly cooled from the above-the upper critical temperature.

It is accordingly an object of this invention to the cobalt and titanium tests based on the following steels'are included herein:

2 Ti f i Type Mn S1 M0 00 Tot 1 uble a 11 21 10 4% 002 l 012 .12 14 v. 10 44 009 013 45 12 067 44 007 27 MO-CO-Tl 11 27 093 42 l 006 29 44 MO-CO-Ti 10 21 11 22 004 52 6 [MU-CU-Ti 11 I 25 14 61 26 28 "The mechanical properties of these steels determined on 1" square bars normalized by holding for 15 minutes at 1700 F. followed by air cooling and-machined'into standard 0.505 round testbars and V-notch Charpy impact specimens are given, in the following, Table A,

Table A.

Tensile Yield Elongar Reduc- T pa Strength, Point, tion,Pertion of Impact,

lbs/inch lbs/inch centin Area, .llbs. square square 2" Percent 56, 780 43, 865 37.0 67. 9 135 C-M 60,795 41, 780 35.3 70.1 139 Mo-C0 59, 670 40. 030 36. 5 70 5 76 MoTi 050 49, 200 31. 8 75. 5 80 Mo-Co-TL 65, 795 47, 350 33. 3 77. 8 186 Mo-Co-Ti. 63, 310 705 33. 5 79. l 201 Mo-Co-Ti. 61, 950 41, 650 35. 2 74. 3 218 provide a molybdenum steel oi the type designed for high temperature steel which has a greatly reduced hardenability.

It is a further object to provide a molybdenumbearing steel of the type designed for high temperature service having a reduced hardenability which is economical to produce.

I have discovered that the foregoing and further objects can be obtained by alloying both Figures of the above table show that the impact strength of Mo-Co-Ti group of alloys is far superior to that of all other steels, while the tensile strength, yield point, elongation, and reduction of area may be considered as being within the generally similar ranges.

Creep-test results obtained on some 01. the above steels are given in the following Table B.

Table B T Stress ior f Stress for ype creep ra e o ru ture in Steel o 001%lhour 1,080 hours at 1,000 F at 1,000 F.

lbs/in. lbs/in.

It can be seen from this tabulation that molybdenum cobalt steel leads other alloys from the standpoint of creep properties, carbon steel is at the bottom of the list and the remaining alloys specific embodiments of my invention, it will be understood that these embodiments are merely for the purpose of illustration and description and that various other forms may be devised occupy an intermediate position. withi n the scope of my invention, as defined in Hardenability characteristics of these steels de- [the appended claim. termined by quenching properly prepared speci- I claim: mens from 1700 F. according to the standard Y A steel of the type designed for high temperapractice recommended by the American Society ture service having reduced hardenability and for Testing Materials (A 255-42T) are listed good impact properties after heating to above below in Table C, giving Rockwell C hardness the upper critical temperature and rapidly coolas a function of the distance from the quenched ing, said steel comprising .05 to carbon, end expressed in sixteenth of an inch. .15 to 50% manganese, .05 to silicon, .40 to Table C Type of Steel Distance 0 C-Mo Mo-Oo Mo-Ti Mo-Oo Ti Mo-Co-Tl Mo -Qo-Ti 1) 7) (2) r c) f (6) 35.5 29.5 18.5 12.5 s 18.5 31 27 11 i ll 18.5 27 2s 14 1 1s 24 l9 12 4 i2 19 15 9 9 16.5 12.5 6 7 14 1o 4 12.5 s 2 11 0.5 10 s An analysis of figures given in the above tabu- -'.60% molybdenum, .25 to .50% titanium, .25 to lation indicates that conventional carbon-molyb- 50% cobalt, balance iron and residual impurities. denum steel exhibits the greatest hardening characteristics and is followed by the molyb- DARWYN BROWN denum-cobalt steel, both of which are definitely more hardenable than the plain carbon steel having the same carbon content. Molybdenumcobalt-titanium alloys show varying hardenimpact strength and resistance to hardening than the conventional steels used for pressurevessel manufacture and accordingly such steels are better adapted for use in such vessels.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,053,346 Merten Sept. 8, 1936 OTHER REFERENCES Titanium in Steel, pages to 197, edited by Comstock et al., published in 1945 by the Pitman While I have shown and described several-------Publishing Corporation, New York. 

